Semiconductor lasers

Abstract

There is disclosed an improved semiconductor laser device ( 10;10 a ), eg a single mode index guided laser diode. The device ( 10;10 a ) comprises: an optical waveguide ( 15;15 a ); at least one electrical contact ( 20;20 a ) extending along part of a length of the waveguide ( 15;15 a ); and wherein the at least one electrical contact ( 20;20 a ) is shorter than the optical waveguide ( 15;15 a ). By this arrangement a part or parts of the waveguide ( 15;15 a ) are not electrically pumped, in use.

What is claimed is:  
     
       1. A semiconductor laser device comprising: 
       a substrate, a first cladding layer formed on the substrate, a core or guiding layer comprising active lasing material and formed on the first cladding layer, a second cladding layer formed on the core or guiding layer;  
       an index-confined optical waveguide having a width, providing lateral optical confinement and extending longitudinally from a first end of the device to a second position between the first end and a second end of the device;  
       an optically active region disposed in the core or guiding layer beneath and/or within the waveguide and extending longitudinally to a third position between the first end of the device and the second position, an electrical contact disposed above the waveguide and extending longitudinally to have an end at the third position;  
       a first optically passive region of the core or guiding layer extending from the second position to the second end of the device, a width of the first optically passive region being broader than the width of the waveguide such that, in use, an optical output from the waveguide diffracts upon traversing the first optically passive region; and  
       a second optically passive region within the core or guiding layer of the device longitudinally extending from the third position to the second position and having said width of the waveguide, the waveguide from the third position to the second position being contact-free.  
     
     
       2. A semiconductor laser device as claimed in  claim 1 , wherein a ridge is formed in at least the second cladding layer and extends longitudinally from the first end of the device to the second position between the first end and the second end of the device. 
     
     
       3. A semiconductor laser device as claimed in  claim 2 , wherein the second optically passive region is part of the ridge. 
     
     
       4. A semiconductor laser device as claimed in  claim 2 , wherein a length from the second position to the second end of the device is around three orders of magnitude smaller than a length between the first and second ends of the device. 
     
     
       5. A semiconductor laser device as claimed in  claim 1 , wherein the core or guiding layer includes a Quantum Well (QW) structure. 
     
     
       6. A semiconductor laser device as claimed in  claim 1 , wherein the first optically passive region comprises a first compositionally disordered or Quantum Well Intermixed (QWI) region provided from the second position to the second end of the device. 
     
     
       7. A semiconductor laser device as claimed in  claim 6 , and further comprising second compositionally disordered or QWI regions laterally bounding the optical active region. 
     
     
       8. A semiconductor laser device as claimed in  claim 7 , wherein the first and second compositionally disordered or QWI regions have substantially the same bandgap. 
     
     
       9. A semiconductor laser device as claimed in  claim 6 , wherein the semiconductor laser device has a ridge width of around 1 to 5 μm, a device width of at least three times that of the ridge, a distance between the first and second device ends of around 1-2 mm, a distance between the first end of the device and the second position of around 1.5 mm, the first optically passive region having a length of around 0.5 mm. 
     
     
       10. A semiconductor laser device as claimed in  claim 1 , wherein the device is of a monolithic construction. 
     
     
       11. A semiconductor laser device as claimed in  claim 1 , wherein the second end of the device comprises an output of the semiconductor laser device, the first optically passive region including a compositionally disordered or QWI region which acts, in use, as a diffractive region at the said output of the laser device, so as to reduce an intensity of optical radiation impinging on a facet of said second end of the device by spreading out the optical radiation. 
     
     
       12. A semiconductor laser device as claimed in  claim 11 , wherein the facet includes an anti-reflective coating on cleaved semiconductor. 
     
     
       13. A semiconductor laser device as claimed in  claim 1 , wherein the semiconductor laser device is fabricated in a III-V semiconductor materials system. 
     
     
       14. A semiconductor laser device as claimed in  claim 13 , wherein the III-V semiconductor materials system is a Gallium Arsenide (GaAs) based system lasing at a wavelength of substantially between 600 and 1300 nm. 
     
     
       15. A semiconductor laser device as claimed in  claim 14 , wherein the first optically passive region includes a first compositionally disordered region, sides of the optical waveguide between first and second ends thereof being bounded by second compositionally disordered regions, the first and second compositionally disordered regions comprising Indium Gallium Arsenide (InGaAs). 
     
     
       16. A semiconductor laser device as claimed in  claim 13 , wherein the III-V semiconductor materials system is an Indium Phosphide (InP) based system lasing at a wavelength of substantially between 1200 and 1700 nm.